1. Field of the Invention
This invention relates to a method and apparatus for forming an aluminum can and, more particularly, pertains to a novel method and apparatus for forming an aluminum container which has a metallic insert incorporated into one end thereof.
The present inventive arrangement effectively provides a novel apparatus and method for providing a compatible welding surface at one end of an extruded aluminum container. A metallic insert is incorporated into an end of an extruded container by placing the insert into an extrusion die prior to extrusion. The present invention is particularly adapted for battery containers and, in particular, for providing a dissimilar welding surface for spot-welding intercell connectors to the extruded aluminum can.
2. Description of the Prior Art
It is well known that cans, particularly cans made of aluminum, can be formed by a variety of processes. One method for producing such a can which additionally has an integrally formed bottom wall, is by, shaping an aluminum sheet blank into a receptacle having a conical circumferential wall by using cooperating dies to squeeze and thin the central portion of the blank and simultaneously radially extruding the surplus metal into a receptacle configuration. This configuration is then placed on a mandrel having the desired inside dimensions of the can body. A spinning operation then takes place to further form the can to the desired shape. As disclosed in Fraze, U.S. Pat. No. 3,572,27l, this method, although relatively complex, does produce cans having an integrally formed bottom wall.
Another method for producing cans, much simpler than the method previously described, is by extruding a metallic slug with a punch and die arrangement. Typically, a disc, or slug, normally consisting of aluminum, is placed into a die with a punch subsequently being forced into the die thereby causing extreme plastic deformation of the slug and extruding the slug into the shape of the die. As disclosed in Siemonsen, U.S. Pat. No. 3,232,260, this type of extrusion formation produces cans having a raw edge and an opposing end which is relatively flat. The methods described hereinabove, although successful in forming aluminum cans, do not address the particular problems to which the present invention is directed.
As is well known in the electrochemical battery art, spot welding of steel intercell connectors to battery cells which have an aluminum cell container is extremely difficult. Spot-welding of the intercell connectors, which are normally comprised of steel or similar metal, to the aluminum cell is inhibited by the aluminum oxide film inherently present on the surface of the aluminum container or housing. In order to effectively bond the intercell connector to the aluminum housing, the oxide film must be somehow removed prior to, or during, the welding operation.
In response to this need of attaching intercell connectors to an extruded aluminum battery cell, ultrasonic welding, a method well known in the prior art, has been adapted for use in the electrochemical battery cell art. To weld a metal intercell connector to the aluminum housing, the housing is first formed by any of the methods described hereinabove. In a secondary operation, which also requires the cell container to be totally empty of electrochemical components, the connector is ultrasonically welded to the base of the aluminum cell. A pressure mandrel is inserted within the aluminum cell housing to resist the force of the externally applied ultrasonic vibrations which vibrate the steel plate, which is to be welded thereto, and aluminum housing the vibrations causing the formation of an effective bond. Ultrasonic welding, considered to be a form of cold welding, applies vibratory energy to the container by a transducer which is arranged to produce shear vibrations at the interface of the parts to be welded. A solid-state bond occur by rupture of the aluminum oxide film and subsequent localized plastic deformation with interpenetration of the metals taking place.
However, the secondary ultrasonic welding operation greatly increases the per item cost of each unit so-produced because it is a time-consuming operation and additionally, because the cell itself must be prepared (i.e. the removal of all electrochemical components), and the entire method is considerably more complex and more lengthy than the more desirable spot-welding operation. Consequently, the present inventive concept provides a relatively simple solution to the problem of providing an integrally formed compatible welding surface to the aluminum housing to allow another metal, and particularly intercell connectors, to be easily and inexpensively spot welded to the aluminum can. None of the prior art, of which Oliver U.S. Pat. No. 2,490,598; Schaefer U.S. Pat. No. 3,981,743; and Jammet U.S. Pat. No. 3,433,681 are typical, show or even suggest the method and apparatus as described herein. Oliver, U.S. Pat. No. 2,490,598, is typically illustrative of spot welding a metal disc to a metal can. However, Oliver is completely silent with respect to the aforedescribed problems associated with the fabrication of aluminum containers.
Schaefer, U.S. Pat. No. 3,981, 743, discloses a lithium-aluminum negative electrode and a method for making same. The patent discloses a sandwich type configuration which is heat soaked while pressure is simultaneously applied to the aluminum-lithium-aluminum configuration thereby causing the lithium and aluminum to chemically react to form a lithium-aluminum alloy. Although Schaefer discloses the use of pressure to bond the dissimilar metals, the extrusion method of the instant invention is believed to be wholly different from this reference. Particularly, this reference is drawn to forming a particular type of electrode, a result to which the present invention is not directed. Further, there is no teaching of the particular problems associated with the spot welding of connectors to the aluminum cell of the battery.
Jammet, U.S. Pat. No. 3,433,681, discloses a typical leakproof electrochemical cell having a sealing cup compressed about the bottom of a metal cup to compensate for the expansion of the cell due to the exhaust gases released while the cell is active. Although not believed to be overly pertinent to the present invention, this reference is included to show the general state of the art related to electrochemical cells.